The problem is that one person cannot possibly learn about everything. One has to make choices. If you spend time learning graphical design rules, you cannot use that time to learn some new algorithm, or how to do business, or some other thing life asks of you. The idea that everyone can be a jack of all trades is equally misguided. I agree that learning everything around your trade up to a certain level is a good idea (to have a clue what people are talking about), but people that specialize in an area tend to underestimate how much time it took them to become experienced in that area, and trivialize how easy others can learn to be adept in their area of expertise.